The present invention relates to hydrazine analyzers and more particularly to hydrazine analyzers wherein the hydrazine is measured by utilizing its tendency to create an electrochemical reaction with a platinum wire under oxidizing conditions.
Hydrazine is added to boiler feed water to improve the life and operation of the equipment by controlling dissolved oxygen concentration. Thus, it is desirable to have reliable equipment capable of accurately detecting the quantity of hydrazine present in the feed water at any particular time. Preferably, the hydrazine is detected on a continuing basis so that the measurement can be used as the input to a feedback loop controlling the rate at which hydrazine is injected into the feed water. Typical prior art devices used for this purpose are shown in the U.S. Pat. Nos. to Haller (2,651,612), and Weingarten (3,694,338). Such prior devices for the detection of hydrazine have generally embodied an elongated, porous, closed end tube having a noble metal electrode (typically of platinum) wound about the outer surface, a silver inner electrode extending into the porous tube which has been filled with a silver oxide or silver chloride salt, and means for feeding an electrolyte into the tube. The electrolyte in combination with the salt creates an internal filling solution forming a half cell on the interior of the tube. The electrolyte solution further passes from the inside of the porous tube through to the outside thereof to contact the external metal electrode. With this arrangement, a gas or liquid containing hydrazine contacting the external electrode produces an electrochemical reaction which causes a voltage to be developed between the electrodes proportional to the quantity of hydrazine present. This voltage can then be detected and displayed by a suitable indicator. Since the salt in the porous tube is generally in the form of a powder poured into the tube and about the silver electrode, the life of the cell is limited to the time elapsed until the salt has washed out of the tube so that the required internal filling solution for the reference half cell is no longer present. The cell then has to be discarded or refilled, if possible. In order to prevent this, the patent to Weingarten teaches that it is desirable to insert the internal half cell within a separate porous enclosure contained within or in close adjacent communicating relationship with the inside of the porous tube.
In all cases, however, the interface between the electrolyte, sample solution, and platinum electrode only occurs at the surface of the porous tube having the platinum outer electrode wound thereon. Flow rates of the sample past the electrode, flow rate of the electrolyte solution from the inside of the tube to the external surface thereof, and the like, are critical factors in the electrochemical reaction taking place at the surface of the porous tube. For example, if the flow rate of the sample does not create a washing of the surface of the tube as in the case when there is no flow, a layer of electrolyte or previously reacted sample can build up surrounding the electrode at the surface of the tube wherein the sample is no longer in contact with the electrode and no, or a reduced, electrochemical reaction is thereby caused to take place. Likewise, if insufficient electrolyte is present at the surface of the porous tube, no, or a reduced, electrochemical reaction is thereby caused to take place.
Therefore, it is the object of the present invention to provide an improved hydrazine analyzer of the general type described wherein the loss of salt from the reference half cell is virtually eliminated and constant conditions for sample-electrolyte interaction with the platinum electrode are present.